Former Newcastle United keeper Harper, who played under Poyet on loan at Brighton, said the 45-year-old was destined to manage at the top level.
Harper said: "I enjoyed my brief time at Brighton and Gus Poyet played a big part in that. He was very impressive.
"He will want Sunderland to play total football, playing out from the back beginning with the goalkeeper because he encourages his players to go out and express themselves.
"He wasn't scared to let players know where they were going wrong or when they weren't doing what he expected of them, but he was approachable and friendly and tactically astute with it. He would join in with training on a Friday afternoon - he wasn't shy about doing a demo and he was still good, too - and sessions were hard work but enjoyable.
"He is a likable man. I know that Sunderland's players will like working with him and I could tell from the start that he was destined to go on and do a big job in the Premier League. He hoped to do that with Brighton, of course, but I'm not surprised that he's getting his chance now.
"It feels like the North East can chew managers up sometimes - I had about 300 of them during my time at Newcastle - but I think he's got the character to do well. It certainly won't faze him. When you're a manager you want to be in the Premier League and he'll relish the opportunity he's been given."
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